The present invention relates to a device that provides an indication of the pressure that existed within a pressure vessel just prior to its being opened or depressurized. More particularly, the present invention is useful in occupant safety restraint systems employing pressure vessels such as those used in a hybrid inflator.
Hybrid inflators typically include a pressure vessel having a quantity of stored gas under pressure. If the stored gas leaked out of the pressure vessel there may not be a sufficient quantity of gas therein to adequately inflate an air bag. Some hybrid inflators include a low pressure switch or sensor to generate a warning signal to the driver, in the event that its internal pressure dropped as a result of losing some quantity of gas. Pressure switches include wires which extend through openings in the pressure vessel. These openings are appropriately sealed using a glass to metal seal of known variety. As can be appreciated these wires, opening and seal may create a potential leak path if they are not correctly sealed. The pressure switch signal, via electronic circuitry provides an indication to the vehicle occupant that the inflator may not be in an operative condition and that repair or replacement may be needed. History and experience have shown that the use of a low pressure switch is unnecessary. If the pressure switch or sensor is eliminated it might still be desirable to provide an indication that the pressure vessel, i.e. the hybrid inflator, was properly pressurized prior to an accident, that is, it contained a sufficient amount of pressurized gas to inflate an air bag.
It is the object of the present invention to provide a device for use within a hybrid inflator that will provide a post depressurization, or "tell tale", indication of inflator function. An additional object of the present invention, is to provide an hybrid inflator having a higher degree of reliability against leakage than one that includes a pressure switch.
Accordingly, the invention comprises: a post depressurization device for providing an indication of the pressure that existed within a fluid filled pressure vessel just prior to depressurization of the pressure vessel, comprising: a housing and piston means for temporarily sealing an open end of the housing and outwardly movable in response to a pressure differential, not less then a predetermined level, that is generated subsequent to the depressurization of the pressure vessel. The piston means and the housing cooperate to define a pressure storage cavity bounded by the piston and housing. The housing including valve means, such as an orifice or check valve for permitting the fluid within the pressure vessel to enter the pressure cavity and stabilize at a level substantially equal to the pressure level within the pressure vessel and for inhibiting a rapid decrease in the pressure within the pressure cavity immediately subsequent to depressurization of the pressure vessel. A frangible member may be used to connect the piston to the housing. This member breaks in response to an applied force of predetermined magnitude to permit the piston to move outwardly in response to the pressure differential.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.